Israeli air strikes on the Gaza Strip continued on December 28 with at least 280 people killed since the offensive began a day earlier.

Israel says the attacks are a response to rocket and mortar fire by Gaza militants, which increased after a six-month cease-fire ended recently.

The UN Security Council and world leaders have called for an immediate end to the violence.

There is widespread panic and confusion on the streets of Gaza, as hospitals and emergency workers struggle to deal with the dead and wounded.

According to Palestinian medical officials, 280 people been killed and up to 700 more wounded.

Most of the dead are reportedly members of the Hamas security forces, but Palestinian officials say there have also been civilian casualties. Militants in Gaza often operate and fire weapons from civilian areas.

Hamas has been in power in Gaza for the last 18 months, after winning parliamentary elections in 2006. The group has been largely shunned by Western powers for its refusal to renounce violence and recognize Israel.

Hamas leader Ismail Haniyah said that "Palestine has never seen an uglier massacre" and said Hamas would launch revenge attacks, which would include suicide bombings inside Israel.

Rocket Attacks

Israel has said the air strikes are a response to almost daily rocket and mortar attacks by Gaza militants, which have intensified after a six-month truce expired eight days ago.

The Israeli Army has said that militants have fired up to 300 rockets and mortars at Israeli targets over the past week. One man was killed and six wounded by a rocket strike in the southern Israeli town of Netivot.

Israeli Defense Minister Ehud Barak said on December 27 that "there is a time for calm and a time for fighting, and now the time has come to fight." Israeli officials have also said Hamas leaders could be targeted in the strikes.

Israel has bolstered infantry troops and armor along the border with the Gaza Strip.

Humanitarian Fears

World leaders have called for an end to the violence, amid fears of an humanitarian crisis. Many Gazans are reliant on food aid and medical supplies are running short.

In a statement early on December 28 after emergency talks, the UN Security Council called for an immediate end to the violence and urged all parties to take necessary measures to prevent a humanitarian crisis, including opening border crossings to allow food and aid to get through.

Arab League Secretary-General Amr Moussa has said that the violence should stop.

Speaking at the Vatican on December 28, Pope Benedict XVI also denounced the violence.

"I ask for a show of humanity and wisdom among those responsible in this situation. I ask the international community to not leave any stone unturned to help the Israelis and Palestinians to turn away from this dead end and to not resign themselves to the perverse logic of conflict and violence, but to favor instead the path of dialogue and negotiations," he said.

Iran's Supreme Leader Ayatollah Ali Khamenei urged Muslim states to punish Israel and deplored what he called some Arab leaders' silence in the face of deadly attacks on the Gaza Strip.

Israel's closest ally, the United States, has blamed Hamas for the outbreak of violence.

Speaking late on December 27, White House spokesperson Gordon Johndroe accused Hamas of breaking the ceasefire and urged Israel to avoid civilian casualties.